Coulomb's law is a law of physics describing the electrostatic interaction between electrically charged particles. It was studied and first published in 1783 by French physicist Charles Augustin de Coulomb and was essential for the development of the theory of electromagnetism.
It deals with the force a point charge exerts on another point charge. A point charge means a charge that is located on a body whose dimensions are much smaller than other relevant dimensions. For example, a collection of electric charges on a pinhead can be regarded as a point charge. Charges are generally measured in coulombs(C). One coulomb is approximately equivalent to 6 X 1018 electrons; it is a very large unit of charge because one electron charge e= -1.6019x10-19 C.
Coulomb's law states that the force between two point charges Q1 and Q2 is:
1. Along the line joining them
2. Directly proportional to the product Q1Q2 of the charges
3. Inversely proportional to the square of the distance R between them.
F = kQ1Q2/R2
The following video may help you to better understand the basic concepts of coloumb's law.